The increasingly pervasive presence of microprocessors in controls has created an increasing demand for sensors in all types of environments so that processes may be more closely monitored, operations may be more finely tuned, and so that efficiencies and emissions may be improved.
Commercially available silicon pressure sensors become unreliable above 200.degree. C. Silicon on Insulator technology has enabled device operation to 300.degree. C., and with costly integrated cooling systems this upper temperature limit has further increased. Large scale production is inhibited by the small size of applicable SiC wafers due to incompatability with conventional semiconductor fabrication facilities.
U.S. Pat. Nos. 5,349,207 and 5,441,911 issued to S. Malhi disclose a structure of SiC bonded to silicon and a method capable of using existing (large) silicon wafer production facilities. One problem with Malhi's structure is that its thermal budget is limited by the silicon substrate. The mismatch in coefficient of thermal expansion between SiC and silicon has the potential to create reliability problems. Another inherent problem with Malhi's structure is that the SiC wafers cannot be precisely and consistently positioned on the silicon substrate. Consequently they cannot be tightly packed. They lack much needed process control. Additionally Malhi's wafers must be sufficiently thick to insure they do not break prior to bonding.